1. Field of the Invention
The present invention relates to an intake air amount control apparatus for an engine capable of electrically driving the degree of opening of a valve, and more specifically, it relates to an intake air amount control apparatus for an engine having a function to hold the degree of opening of a valve at a predetermined degree of intermediate opening slightly greater than an idle opening when a drive motor becomes inoperable due to malfunctions such as a conduction defect, etc.
2. Description of the Related Art
In the past, there has been known an intake air amount control apparatus for an engine in which two springs, including a first coiled torsion spring for urging a valve in an intake passage toward a valve opening side and a second coiled torsion spring for urging the valve toward a valve closing side, are used to hold the valve at a predetermined degree of intermediate opening (for example, see a first patent document: Japanese patent application laid-open No. 2-500677, FIG. 1).
However, the known intake air amount control apparatus for an engine as described in the above-mentioned first patent document has the following problems. That is, two springs for urging the valve toward the intermediate opening are required, thus increasing the number of component parts, and the controllability of the valve in its movement from its intermediate opening position toward the closing side or the opening side becomes unstable due to variation in the characteristics of the individual springs.